1. Technical Field
The present disclosure is directed to a device and a method for trimming a capacitor to a precise capacitance, and more particularly, applying heat to alter a dielectric constant of a dielectric layer between parallel plates of the capacitor.
2. Description of the Related Art
A parallel plate capacitor has two conductive plates separated by a dielectric material. The capacitance of the parallel plate capacitor is determined by the following formula:
  C  =                    ɛ        r            ⁢              ɛ        0            ⁢      A        d  where C is the capacitance, ∈r is the dielectric constant (relative permittivity) of the dielectric material between the plates, ∈0 is the electric constant, A is the area of overlap between the plates, and d is the distance between the plates. In order to change the capacitance, the distance between the plates can be changed, the area of overlap can be changed, or the dielectric constant can be changed.
One common technique to change the capacitance of a capacitor in an integrated circuit is laser trimming, for which specific equipment is used to cut away a portion of the capacitor to alter the capacitance. In order to provide for a range of capacitances, the capacitor before trimming is formed over a large area of the silicon substrate. After trimming, any portion of the capacitor that is cut away becomes unused or wasted space.
Laser trimming is performed at wafer level or die level by exposing one of the plates to the laser, which means the capacitance is set before shipment to a consumer. This technique is expensive, utilizes valuable space on the integrated circuit, and does not provide the consumer with flexibility to select the capacitance.